[Elecraft] Balun Questions

[Chuck Catledge]

It’s quite practical to use 25 to 35 mm radius bends of RG400 for large ferrite cores including both the one-piece and the snap-on varieties.  RG400 has the same diameter as RG-58, i.e. 0.195”.  See K9YC’s tutorial here:

http://audiosystemsgroup.com/RFI-Ham.pdf

 

All of the RF common mode chokes I have made using small cable (i.e. RG400 through RG6) use radii of 1-3 inches with the RG6 tending toward 3” and greater due to the foam dielectric.  

---

Chuck, AE4CW

From: Mel Farrer [mailto:farrerfolks at yahoo.com] 
Sent: Sunday, February 07, 2016 17:54
To: Chuck Catledge <ae4cw at att.net>; 'Guy Olinger K2AV' <k2av.guy at gmail.com>; 'Robert Nobis' <n7rjn at nobis.net>
Cc: elecraft at mailman.qth.net; 'Ron D'Eau Claire' <ron at cobi.biz>
Subject: Re: [Elecraft] Balun Questions

 

SORRY, but the min static bending radius for RG-303 is 25 mm and RG-400 is 35 mm.  For torroid wrap which is better?????

 

Mel, K6KBE

 

  _____  

From: Chuck Catledge <ae4cw at att.net <mailto:ae4cw at att.net> >
To: 'Guy Olinger K2AV' <k2av.guy at gmail.com <mailto:k2av.guy at gmail.com> >; 'Robert Nobis' <n7rjn at nobis.net <mailto:n7rjn at nobis.net> > 
Cc: elecraft at mailman.qth.net <mailto:elecraft at mailman.qth.net> ; 'Ron D'Eau Claire' <ron at cobi.biz <mailto:ron at cobi.biz> >
Sent: Sunday, February 7, 2016 2:31 PM
Subject: Re: [Elecraft] Balun Questions


At hamfests around the Southeast, surplus RG400 is often found in terminated cables (usually BNC or N) in lengths up to around 20 feet.  The price I've paid is always less than $1.00 per foot, sometimes much less.  I've used it to make dozens of RF chokes (1:1 baluns).  The small size of RG400 allows the use of a single medium to large clamp-on #31 ferrite that works effectively from 10-160M, conditioned by the number of turns.  The large snap-on ferrite will accommodate 10-12 turns; the medium snap-on will handle 5-6 turns.  Jim, K9YC's tutorials are excellent.  Consult the Fair-Rite website for additional technical data.

BTW, the Teflon dielectric allows easy soldering in PL-259s with RG-58 reducers without any fear of melting the dielectric.
---
Chuck, AE4CW

-----Original Message-----
From: Guy Olinger K2AV [mailto:k2av.guy at gmail.com <mailto:k2av.guy at gmail.com> ] 
Sent: Sunday, February 07, 2016 01:08
To: Robert Nobis <n7rjn at nobis.net <mailto:n7rjn at nobis.net> >
Cc: elecraft at mailman.qth.net <mailto:elecraft at mailman.qth.net> ; Ron D'Eau Claire <ron at cobi.biz <mailto:ron at cobi.biz> >; Guy Olinger K2AV <k2av.guy at gmail.com <mailto:k2av.guy at gmail.com> >
Subject: Re: [Elecraft] Balun Questions

RG303 is not rated for the tight bends.  RG400 with its fine stranded center conductor is rated for corner bends in aircraft wiring harnesses and will not deform the dielectric within the bends. I would not wind any solid center conductor coax on a toroid.

I would only buy cut lengths of RG400 after the lengths for a project are known. Some number of such suppliers on eBay. One currently listed at 1.98 per foot:
http://www.ebay.com/itm/RG400-Coaxial-Cable-Mil-spec-by-the-ft-US-supplier-/251260159394?hash=item3a8045c5a2:g:WpAAAOxy43FRafUe

True it ain't ham cheep. The good stuff that lasts and lasts almost never is. Back in the early days of eBay I came by a 142' length of RG400 for $25. That's $0.178  a foot  I also came by bundles of miscellaneous 6 foot to 15 foot jumpers with various connectors on end for similar ridiculous low prices per foot.

The silvered copper strands stand up to migration of dampness in a way not possible with same size copper strands minus the silvering. I have
*measured* the dry RF resistance at 1.83 MHz of a 67 foot length of corroded #14 stranded plain copper at 62 ohms. When new this wire had resistance at RF of less than an ohm. I have never found the silvered copper equivalent in anything remotely approaching that degraded state.

RG400 wound on the proper core for the job will last a lifetime.

73, Guy K2AV

On Saturday, February 6, 2016, Robert Nobis <n7rjn at nobis.net <mailto:n7rjn at nobis.net> > wrote:

> I have used RG303/U for chokes.  A bit smaller diameter than RG400 
> (0.170 versus 0.195 inches). RG303/U has a solid copper center 
> conductor that is silver plated.  The shield for RG303 is also silver 
> plated copper. The jacket is Class 9 Teflon. Also the dielectric material is teflon.
>
> 73,
>
>
> Bob Nobis - N7RJN
> n7rjn at nobis.net <mailto:n7rjn at nobis.net> 
>
>
> > On Feb 6, 2016, at 17:49, Guy Olinger K2AV <k2av.guy at gmail.com <mailto:k2av.guy at gmail.com> > wrote:
> >
> > If one wants a small 50 ohm coax that will take QRO with a very 
> > large margin and was *designed* for bending and use in aircraft 
> > wiring
> harnesses
> > then use RG400 to wind around your core. RG400 uses a fine stranded 
> > silvered copper center conductor that is more flexible than its 
> > Teflon dielectric. It has a double shield made from silvered copper strands.
> >
>
>
>


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